scholarly journals Rainfall Estimation with an Operational Polarimetric C-Band Radar in the United Kingdom: Comparison with a Gauge Network and Error Analysis

2011 ◽  
Vol 12 (5) ◽  
pp. 935-954 ◽  
Author(s):  
V. N. Bringi ◽  
M. A. Rico-Ramirez ◽  
M. Thurai
Keyword(s):  
United Kingdom ◽  
Rain Rate ◽  
Error Variance ◽  
Absolute Error ◽  
Rain Attenuation ◽  
Statistical Measures ◽  
Composite Estimator ◽  
Using Data ◽  
Radar Rain Rate ◽  
Rain Rates

Abstract The estimate of rainfall using data from an operational dual-polarized C-band radar in convective storms in southeast United Kingdom is compared against a network of gauges. Four different rainfall estimators are considered: reflectivity–rain-rate (Z–R) relation, with and without correcting for rain attenuation; a composite estimator, based on (i) Z–R, (ii) R(Z, Zdr), and (iii) R(Kdp); and exclusively R(Kdp). The various radar rain-rate estimators are developed using Joss disdrometer data from Chilbolton, United Kingdom. Hourly accumulations over radar pixels centered on the gauge locations are compared, with approximately 2500 samples available for gauge hourly accumulations > 0.2 mm. Overall, the composite estimator performed the “best” based on robust statistical measures such as mean absolute error, the Nash–Sutcliffe coefficient, and mean bias, at all rainfall thresholds (>0.2, 1, 3, or 6 mm) with improving measures at the higher thresholds of >3 and >6 mm (higher rain rates). Error variance separation is carried out by estimating the gauge representativeness error using 4 yr of gauge data from the Hydrological Radar Experiment. The proportion of variance of the radar-to-gauge differences that could be explained by the gauge representativeness errors ranged from 20% to 55% (for the composite rain-rate estimator). The radar error is found to decrease from approximately 70% at the lower rain rates to 20% at the higher rain rates. The composite rain-rate estimator performed as well as can be expected from error variance analysis, at mean hourly rain rates of about 5 mm h−1 or larger with mean bias of ~10% (underestimate).

Comparison of measured rain attenuation and ITU-R predictions on experimental microwave links in Malaysia

2011 ◽  
Vol 3 (4) ◽  
pp. 477-483 ◽  
Author(s):  
Amuda Yusuf Abdulrahman ◽  
Tharek bin Abdulrahman ◽  
Sharul Kamal bin Abdulrahim ◽  
Ulaganathen Kesavan
Keyword(s):  
Cumulative Distribution Function ◽  
Rain Rate ◽  
Rain Attenuation ◽  
Rain Gauge ◽  
Cumulative Distribution ◽  
Rain Gauge Data ◽  
Tropical Regions ◽  
International Telecommunication ◽  
Rain Rates ◽  
Rainfall Attenuation

This paper presents the results of direct rain attenuation measurements carried out on four experimental microwave links, installed at UTM, Malaysia. The links operate at frequencies of 15, 22, 26, and 38 GHz and the cumulative distribution function for different rain rates have been generated from the measured 4-year rain gauge data. The experimentally measured attenuation data have been compared with International Telecommunication Unior-R rain attenuation predictions; and it has been found that the latter have underestimated the measured values, especially at higher rain rates. The deviations have been modeled as a function of rain rate exceedances R%p. It is hoped that the study will provide useful information for estimation of rainfall attenuation on microwave links in tropical regions that have similar situation to Malaysia.

scholarly journals Observations of Wintertime U.S. West Coast Precipitating Systems with W-Band Satellite Radar and Other Spaceborne Instruments

2012 ◽  
Vol 13 (1) ◽  
pp. 223-238 ◽  
Author(s):  
Sergey Y. Matrosov
Keyword(s):  
Cross Sections ◽  
West Coast ◽  
Rain Rate ◽  
Water Vapor Transport ◽  
Rainfall Regime ◽  
Mean Values ◽  
W Band ◽  
Satellite Radar ◽  
Using Data ◽  
Rain Rates

Abstract The potential of CloudSat W-band radar for observing wintertime storms affecting the West Coast of North America is evaluated. Storms having high hydrological impact often result from landfalls of “atmospheric rivers” (“ARs”), which are the narrow elongated regions of water vapor transport from the tropics. CloudSat measurements are used for retrievals of rain rate R and cloud ice water path (IWP) along the satellite ground track over ocean and land. These retrievals present quasi-instantaneous vertical cross sections of precipitating systems with high-resolution information about hydrometeors. This information is valuable in coastal areas with complex terrain where observations with existing instrumentation, including ground-based radars, are limited. CloudSat reflectivity enhancements [i.e., bright band (BB)] present a way to estimate freezing levels, indicating transitions between rainfall and snowfall. CloudSat estimates of these levels were validated using data from radiosonde soundings and compared to model and microwave sounder data. Comparisons of CloudSat retrievals of rain rates with estimates from ground-based radars in the areas where measurements from these radars were available indicated an agreement within retrieval uncertainties, which were around 50%. The utility of CloudSat was illustrated for case studies of pronounced AR events at landfall and over ocean. Initial analysis of CloudSat crossings of ARs during the 2006/07 season were used for rainfall regime prevalence assessment. It indicated that stratiform rain, which often had BB features, warm rain, and mixed rain were observed with about 26%, 24%, and 50% frequency. Stratiform regions generally had higher rain rates. Significant correlation (~0.72) between mean values of IWP and rain rate was observed for stratiform rainfall.

Analysis of Raindrop Diameters for Rainfall Attenuation in Southern Africa

2016 ◽  
Vol 6 (1) ◽  
pp. 82
Author(s):  
Oluwumi Adetan ◽  
Obiseye Obiyemi
Keyword(s):  
Shape Parameter ◽  
Rain Rate ◽  
Rain Attenuation ◽  
Specific Attenuation ◽  
Total Percentage ◽  
Raindrop Size Distribution ◽  
Raindrop Size ◽  
Rain Rates ◽  
Rainfall Attenuation ◽  
Rainfall Regimes

The influence of critical raindrop diameters on the specific rainfall attenuation in Durban (29<sup>o</sup>52'S, 30<sup>o</sup>58'E), South Africa using various rainfall regimes is analyzed in this paper. Different rain rate values representing drizzle, widespread, shower and thunderstorm are selected for the purpose of analysis over the measured raindrop size distribution. The three-parameter lognormal and gamma DSD models with shape parameter of 2 are used to estimate the parameters required to investigate the drop sizes which produce a major contribution to the total specific rainfall attenuation for the selected rain rate values. The computed total specific attenuation increases with increasing frequencies and rain rates. The highest and prevailing contribution to the specific attenuation occurs at  for the stratiform (drizzle or widespread) and convective (shower or thunderstorm) rain types for the models considered.  The total percentage fraction formed by drops in the diameter range 0.5 mm ≤ <em>D</em> ≤ 2.5 mm and 1.0 mm ≤<em> D</em> ≤ 3.0<em> </em>mm<em> </em>are found to be most critical for the specific rain attenuation for the stratiform (drizzle and widespread)  and convective (shower and thunderstorm) rainfall types especially at higher frequencies.

scholarly journals Analysis of Raindrop Diameters for Rainfall Attenuation in Southern Africa

2016 ◽  
Vol 6 (1) ◽  
pp. 82
Author(s):  
Oluwumi Adetan ◽  
Obiseye Obiyemi
Keyword(s):  
Shape Parameter ◽  
Rain Rate ◽  
Rain Attenuation ◽  
Specific Attenuation ◽  
Total Percentage ◽  
Raindrop Size Distribution ◽  
Raindrop Size ◽  
Rain Rates ◽  
Rainfall Attenuation ◽  
Rainfall Regimes

The influence of critical raindrop diameters on the specific rainfall attenuation in Durban (29<sup>o</sup>52'S, 30<sup>o</sup>58'E), South Africa using various rainfall regimes is analyzed in this paper. Different rain rate values representing drizzle, widespread, shower and thunderstorm are selected for the purpose of analysis over the measured raindrop size distribution. The three-parameter lognormal and gamma DSD models with shape parameter of 2 are used to estimate the parameters required to investigate the drop sizes which produce a major contribution to the total specific rainfall attenuation for the selected rain rate values. The computed total specific attenuation increases with increasing frequencies and rain rates. The highest and prevailing contribution to the specific attenuation occurs at  for the stratiform (drizzle or widespread) and convective (shower or thunderstorm) rain types for the models considered.  The total percentage fraction formed by drops in the diameter range 0.5 mm ≤ <em>D</em> ≤ 2.5 mm and 1.0 mm ≤<em> D</em> ≤ 3.0<em> </em>mm<em> </em>are found to be most critical for the specific rain attenuation for the stratiform (drizzle and widespread)  and convective (shower and thunderstorm) rainfall types especially at higher frequencies.

scholarly journals Polarimetric Estimates of a 1-Month Accumulation of Light Rain with a 3-cm Wavelength Radar

2011 ◽  
Vol 12 (5) ◽  
pp. 1024-1039 ◽  
Author(s):  
L. Borowska ◽  
D. Zrnić ◽  
A. Ryzhkov ◽  
P. Zhang ◽  
C. Simmer
Keyword(s):  
Rain Rate ◽  
Rain Gauge ◽  
Light Rain ◽  
Differential Phase ◽  
Rain Gauges ◽  
Bright Band ◽  
X Band ◽  
Wet Snow ◽  
Composite Estimator ◽  
Rain Rates

Abstract The authors evaluate rainfall estimates from the new polarimetric X-band radar at Bonn, Germany, for a period between mid-November and the end of December 2009 by comparison with rain gauges. The emphasis is on slightly more than 1-month accumulations over areas minimally affected by beam blockage. The rain regime was characterized by reflectivities mainly below 45 dBZ, maximum observed rain rates of 47 mm h−1, a mean rain rate of 0.1 mm h−1, and brightband altitudes between 0.6 and 2.4 km above the ground. Both the reflectivity factor and the specific differential phase are used to obtain the rain rates. The accuracy of rain total estimates is evaluated from the statistics of the differences between radar and rain gauge measurements. Polarimetry provides improvement in the statistics of reflectivity-based measurements by reducing the bias and RMS errors from −25% to 7% and from 33% to 17%, respectively. Essential to this improvement is separation of the data into those attributed to pure rain, those from the bright band, and those due to nonmeteorological scatterers. A type-specific (rain or wet snow) relation is applied to obtain the rain rate by matching on the average the contribution by wet snow to the radar-measured rainfall below the bright band. The measurement of rain using specific differential phase is the most robust and can be applied to the very low rain rates and still produce credible accumulation estimates characterized with a standard deviation of 11% but a bias of −25%. A composite estimator is also tested and discussed.

Intercomparisons of CloudSat and Ground-Based Radar Retrievals of Rain Rate over Land

2014 ◽  
Vol 53 (10) ◽  
pp. 2360-2370 ◽  
Author(s):  
Sergey Y. Matrosov
Keyword(s):  
Rain Rate ◽  
Correlation Coefficients ◽  
Stratiform Precipitation ◽  
Radar Measurements ◽  
The Mean ◽  
Satellite Radar ◽  
Mean Differences ◽  
Radar Rain Rate ◽  
Rain Rates ◽  
Precipitation Events

AbstractExperimental retrievals of rain rates using the CloudSat spaceborne 94-GHz radar reflectivity gradient method over land were evaluated by comparing them with standard estimates from ground-based operational S-band radar measurements, which are widely used for quantitative precipitation estimations. The comparisons were performed for predominantly stratiform precipitation events that occurred in the vicinity of the Weather Surveillance Radar-1988 Doppler (WSR-88D) KGWX and KSHV radars during the CloudSat overpasses in the vicinity of these ground radar sites. The standard reflectivity-based WSR-88D rain-rate retrievals used in operational practice were utilized as a reference for the CloudSat retrieval evaluation. Spaceborne and ground-based radar rain-rate estimates that were closely collocated in space and time were generally well correlated. The correlation coefficients were approximately 0.65 on average, and the mean relative biases were usually within ±35% for the whole dataset and for individual events with typical rain rates exceeding ~2 mm h−1. For events with lighter rainfall, higher biases and lower correlations were often present. The normalized mean absolute differences between satellite- and ground-based radar retrievals were on average ~60%, with an increasing trend for lighter rainfall. Such mean differences are comparable to combined retrieval errors from both ground-based and satellite radar remote sensing approaches. Evaluation of potential effects of partial beam blockage on the ground-based radar measurements was performed, and the influence of the choice of relation between WSR-88D reflectivity and rain rate that was utilized in the ground-based rain-rate retrievals was assessed.

scholarly journals Precipitation estimation over radar gap areas based on satellite and adjacent radar observations

2014 ◽  
Vol 7 (6) ◽  
pp. 6299-6325 ◽  
Author(s):  
Y.-R. Lee ◽  
D.-B. Shin ◽  
J.-H. Kim ◽  
H.-S. Park
Keyword(s):  
Rain Rate ◽  
A Priori ◽  
Geostationary Satellite ◽  
Observation Data ◽  
Satellite Precipitation ◽  
Brightness Temperatures ◽  
Precipitation Estimation ◽  
Precipitation Estimates ◽  
Using Data ◽  
Radar Rain Rate

Abstract. Continuous rainfall measurements from ground-based radars are crucial for monitoring and forecasting heavy rainfall-related events such as floods and landslides. However, complete coverage by ground-based radars is often hampered by terrain blockage and beam-related errors. In this study, we presented a method to fill the radar gap using surrounding radar-estimated precipitation and observations from a geostationary satellite. The method first estimated the precipitation over radar gap areas using data from the Communication, Ocean, and Meteorological Satellite (COMS); the first geostationary satellite of Korea. The initial precipitation estimation from COMS was based on the rain rate-brightness temperature relationships of a priori databases. The databases were built with the temporally and spatially collocated brightness temperatures at four channels (3.7, 6.7, 10.8, and 12 μm) and Jindo (126.3° E, 34.5° N) radar rain rate observations. The databases were updated with collocated datasets in a timespan of approximately one hour prior to the designated retrieval. Then, bias correction based on an ensemble bias factor field (Tesfagiorgis et al., 2011b) from radar precipitation was applied to the estimated precipitation field. Over the radar gap areas, this method finally merged the bias corrected satellite precipitation with the radar precipitation obtained by interpolating the adjacent radar observation data. The merging was based on the optimal weights that were determined from the root-mean-square error (RMSE) with the reference sensor observation or equal weights in the absence of reference data. This method was tested for major precipitation events during the summer of 2011 with assumed radar gap areas. The results suggested that successful merging appears to be closely related to the quality of the satellite precipitation estimates.

scholarly journals Precipitation estimation over radar gap areas based on satellite and adjacent radar observations

2015 ◽  
Vol 8 (2) ◽  
pp. 719-728 ◽  
Author(s):  
Y.-R. Lee ◽  
D.-B. Shin ◽  
J.-H. Kim ◽  
H.-S. Park
Keyword(s):  
Rain Rate ◽  
A Priori ◽  
Geostationary Satellite ◽  
Observation Data ◽  
Satellite Precipitation ◽  
Brightness Temperatures ◽  
Precipitation Estimation ◽  
Precipitation Estimates ◽  
Using Data ◽  
Radar Rain Rate

Abstract. Continuous rainfall measurements from ground-based radars are crucial for monitoring and forecasting heavy rainfall-related events such as floods and landslides. However, complete coverage by ground-based radars is often hampered by terrain blockage and beam-related errors. In this study, we presented a method to fill the radar gap using surrounding radar-estimated precipitation and observations from a geostationary satellite. The method first estimated the precipitation over radar gap areas using data from the Communication, Ocean, and Meteorological Satellite (COMS); the first geostationary satellite of Korea. The initial precipitation estimation from COMS was based on the rain rate-brightness temperature relationships of a priori databases. The databases were built with temporally and spatially collocated brightness temperatures at four channels (3.7, 6.7, 10.8, and 12 μm) and Jindo (126.3° E, 34.5° N) radar rain rate observations. The databases were updated with collocated data sets in a timespan of approximately one hour prior to the designated retrieval. Then, bias correction based on an ensemble bias factor field (Tesfagiorgis et al., 2011b) from radar precipitation was applied to the estimated precipitation field. Over the radar gap areas, this method finally merged the bias-corrected satellite precipitation with the radar precipitation obtained by interpolating the adjacent radar observation data. The merging was based on optimal weights determined from the root-mean-square error (RMSE) with the reference sensor observation or equal weights in the absence of reference data. This method was tested for major precipitation events during the summer of 2011 with assumed radar gap areas. The results suggested that successful merging appears to be closely related to the quality of the satellite precipitation estimates.

scholarly journals Estimating Rain Rates from Tipping-Bucket Rain Gauge Measurements

2008 ◽  
Vol 25 (1) ◽  
pp. 43-56 ◽  
Author(s):  
Jianxin Wang ◽  
Brad L. Fisher ◽  
David B. Wolff
Keyword(s):  
Rain Rate ◽  
Tropical Rainfall Measuring Mission ◽  
Rain Gauge ◽  
Radar Reflectivity ◽  
Time Shift ◽  
Estimation Errors ◽  
Rate Estimation ◽  
Reflectivity Data ◽  
Rain Rates ◽  
Event Definition

Abstract This paper describes the cubic spline–based operational system for the generation of the Tropical Rainfall Measuring Mission (TRMM) 1-min rain-rate product 2A-56 from tipping-bucket (TB) gauge measurements. A simulated TB gauge from a Joss–Waldvogel disdrometer is employed to evaluate the errors of the TB rain-rate estimation. These errors are very sensitive to the time scale of rain rates. One-minute rain rates suffer substantial errors, especially at low rain rates. When 1-min rain rates are averaged over 4–7-min intervals or longer, the errors dramatically reduce. Estimated lower rain rates are sensitive to the event definition whereas the higher rates are not. The median relative absolute errors are about 22% and 32% for 1-min rain rates higher and lower than 3 mm h−1, respectively. These errors decrease to 5% and 14% when rain rates are used at the 7-min scale. The radar reflectivity–rain-rate distributions drawn from the large amount of 7-min rain rates and radar reflectivity data are mostly insensitive to the event definition. The time shift due to inaccurate clocks can also cause rain-rate estimation errors, which increase with the shifted time length. Finally, some recommendations are proposed for possible improvements of rainfall measurements and rain-rate estimations.

Migration Processes among the Highly Skilled in Europe

1992 ◽  
Vol 26 (2) ◽  
pp. 484-505 ◽  
Author(s):  
John Salt
Keyword(s):  
United Kingdom ◽  
Skilled Workers ◽  
Migration Process ◽  
The United Kingdom ◽  
Highly Skilled ◽  
European Business ◽  
Business Structures ◽  
Using Data ◽  
Corporate Business ◽  
Official Sources

This article seeks to show that the migration process for highly skilled workers in contemporary Europe is part of the structuring of European business. It focuses on the employer's perspective and role in articulating movement, using data from various official sources as well as survey evidence from the United Kingdom. It suggests that the increasing importance of this form of mobility is related to the process of internationalization by large employers and that the particular form of movement is dependent on the evolution of corporate business structures.

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